1. Field of the Invention
The present invention relates to a cable modem, in particular to a cable modem having a pattern matching system for quick and flexible determinations concerning actions to take regarding frames of the cable modem.
2. Description of the Related Art
In recent years, cable television networks have become widespread. A typical cable television system can carry many television stations, and is effectively a high bandwidth system. Because of the increasing availability of cable television infrastructure, the use of television cables as the medium for computer data networks has the potential for giving users high bandwidth at a reasonable cost. A cable television system, however, requires several enhancements in order to function as a data network.
In its classic form, a cable television system carries information in only one direction from the cable system headend to the individual user. The user interface to the system generally comprises a receiver such as a television or a stereo. The headend transmits television or stereo channels simultaneously. In general, the user has no influence on what is transmitted and can only choose among the channels the headend is transmitting.
In contrast, a data network carries data from the headend to the user (the downstream path) and from the user to the headend (the upstream path). The individual user requires equipment, such as a cable modem, that can both receive from the headend and transmit to it. A cable data network must be able to handle many individual users simultaneously, each of whom have control over what they receive and transmit.
Cable modems offer greatly improved bandwidth capable of delivering services hundreds, or even thousands, of times faster than conventional modems. Cable modems can achieve data-transfer rates of up to 40 Mbits/s by connecting directly to coaxial lines as opposed to dial-in modems that use twisted-pair copper telephone lines.
In order for a cable television network to operate as a data network, it requires a headend capable of both transmitting and receiving data. To ensure that each user receives the data they require, a network protocol must be implemented to allow independent users of the network to utilize the shared headend and the distribution network without interference from or receiving the data of other users.
The network protocol places requirements on both the headend and the user end. Generally, the headend serves as the network controller, and the user's cable modem must be able to respond to commands from the headend. In cable modems adhering to the well-known OSI reference model, the lowest layer is the Physical layer (PHY), while the next layer up is the Data Link layer. The Data Link layer is segmented into two parts, the Medium Access Controller (MAC), which interfaces with the PHY, and the Logical Link Control (LLC), which interfaces to the MAC and to higher layers. In general, the MAC and LLC provide the following Data Link functionality: transmit and receive data encapsulation, including framing (frame boundary delineation, frame synchronization), addressing (management of source and destination address), and error detection (detection of physical medium transmission errors); and media access management, including collision avoidance and handling. A physical address or MAC address is a unique Data Link layer address that is assigned to every port or device that connects to a network. Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures.
In an effort to coordinate the development of multimedia high-speed data services and the interoperability of network devices, cable operators have formed the Multimedia Cable Network Systems (MCNS) Group in cooperation with the industry research and development consortium CableLabs. The MCNS group has promulgated the Data Over Cable Service Interface Specification (DOCSIS). Other standards utilizing transport frames, such as DAVIC/DVB, have likewise been created. Such standards continue to evolve over time, with the frequent inclusion of additional feature sets. In specifications such as DOCSIS, MAC-layer frames are encapsulated in transport-layer frames, such as MPEG frames.
The term “cable modem termination system” (CMTS) generally refers to a cable bridge or cable router in the cable head-end. A CMTS acts as the master station in a DOCSIS-compliant cable data system. The CMTS is generally the only station that transmits downstream, and it controls the scheduling of upstream transmissions by associated cable modems.
In a shared network, such as a cable modem network deployed over a large residential area, upstream and downstream data could be intercepted and read by anyone along the path between a specific cable modem and the cable head-end. Accordingly, some form of security is needed to protect those cable system operators, as well as owners of intellectual property from theft or denial of service. The MCNS specification attempts to address these needs by providing for privacy, authentication, and service integrity through the use of strong cryptography.
In addition, data that is received at a cable modem often consumes processing time from the cable modem. The processing time is wasted if the data is not of any use to the cable modem. Thus, early detection of data relevance is desired. This detection could occur by matching certain patterns in the data, e.g., MAC addresses, IP addresses, etc., with predetermined patterns. Software implementations of this pattern matching are unacceptably slow and hardware implementations are inflexible.
Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.